This invention relates generally to gas turbine engine turbines and more particularly to methods for cooling turbine sections of such engines.
A gas turbine engine includes a turbomachinery core having a high pressure compressor, a combustor, and a high pressure or gas generator turbine in serial flow relationship. The core is operable in a known manner to generate a primary gas flow. In a turbojet or turbofan engine, the core exhaust gas is directed through an exhaust nozzle to generate thrust. A turboshaft engine uses a low pressure or “work” turbine downstream of the core to extract energy from the primary flow to drive a shaft or other mechanical load.
The gas generator turbine includes annular arrays of stationary vanes or nozzles that direct the gases exiting the combustor into rotating blades or buckets. Collectively one row of nozzles and one row of blades make up a “stage”. Typically two or more stages are used in serial flow relationship. These components operate in an extremely high temperature environment, and must be cooled by air flow to ensure adequate service life. Typically, the air used for cooling is extracted from one or more points in the compressor. These bleed flows represent a loss of net work output and/or thrust to the thermodynamic cycle. They increase specific fuel consumption (SFC) and are generally to be avoided as much as possible.
Typical prior art two stage turbines use high pressure compressor discharge air (referred to as “CDP air”) to cool the first stage turbine nozzle and first stage shroud, and lower pressure inter-stage or impeller tip bleed to cool the second stage turbine nozzle and second stage turbine shroud. In this case, no distinction is made between the nozzle airfoil and the nozzle cavities, even though these areas have different requirements for cooling air pressure and flow. This results in bleed air losses that are greater than the minimum required.